Diamond sintered body having high strength and high wear resistance, and tool including the same

ABSTRACT

A diamond sintered body having high wear resistance, chipping resistance, shock resistance and thermal conductivity is provided. The diamond sintered body includes sintered diamond particles and a sintering aid as the remainder. The content of the sintered diamond particles is at least 80% by volume and less than 99% by volume. The sintered diamond particles have a particle size in the range from at least 0.1 μm to at most 70 μm. The sintered diamond particles next to each other are directly bonded. The sintering aid includes at least one kind selected from tungsten, iron, cobalt and nickel. The percentage of the tungsten in the sintered body is in the range from at least 0.01% by weight to at most 8% by weight.

TECHNICAL FIELD

The present invention relates generally to a diamond sintered bodyhaving high strength and high wear resistance, and particularly, to ahighly strong and highly abrasion-resisting diamond sintered body havinghigh wear resistance, chipping resistance, shock resistance and thermalconductivity, and a tool including the sintered body.

BACKGROUND ART

Diamond is the hardest material present on earth. Particularly, adiamond sintered body hardly suffers from chips caused by the cleavage,a shortcoming of monocrystalline diamond, and therefore is often used asa material for a cutting tool for a nonferrous material such as analuminum-silicon alloy. Japanese Patent Publication Nos. 39-20483 and52-12126 for example disclose sintered bodies formed by sinteringdiamond particles using a ferrous metallic binder such as cobalt.

Among these diamond sintered bodies, those having granules with adiamond particle size of less than 5 μm or those having extra finegranules with a particle size of at most 1 m are known as highlychipping-resisting materials. Japanese Patent Publication No. 39-20483for example discloses a diamond sintered body including fine diamondparticles and ferrous metal powder which allows diamond to be dissolvedand re-precipitated, and Japanese Patent Publication No. 58-32224 forexample discloses a diamond sintered body including sintered diamondparticles having a particle size of at most 1 μm, a carbide, a nitrideand a boride of a metal belonging to group 4a, 5a or 6a in the periodictable, a solid solution or mixture thereof and a ferrous alloy.

When these fine diamond particles and a ferrous metal such as cobalt ortungsten carbide-cobalt are used as starting materials for sintering,diamond particles could often grow abnormally unless the temperature andpressure conditions are strictly controlled, because such diamondparticles are extremely active. Therefore, the size of the diamondparticles partly becomes extremely large, which makes it difficult toprovide a diamond sintered body having a particle size of at most 1 μmand a homogeneous microstructure with high yields.

In order to solve this problem, there is known a method of controllingthe growth of particles by providing hard particles such as tungstencarbide, cubic boron nitride and silicon carbide at diamond grainboundaries. Japanese Patent Publication No. 61-58432 for examplediscloses a diamond sintered body formed by adding tungsten carbide ashard particles.

This method however controls abnormal growth of diamond particles byproviding hard particles having low compatibility with diamond particlesbetween the diamond particles, thereby physically and chemicallypreventing direct bonding between the diamond particles, and thereforethe formation of skeletons by sintering between the diamond particles isinsufficient. As a result, the chipping resistance, shock resistance andthermal conductivity, i.e., essential characteristics of diamond aredisadvantageously lowered.

Meanwhile, among various diamond sintered bodies, coarse grained oneshaving a particle size from at least 5 μm to at most 100 μm aregenerally known as having high wear resistance. Such coarse graineddiamond particles are, however, not easily sintered, and therefore aknown method forms a carbide on the surface of diamond particles inorder to make sintering easier. Japanese Patent Laying-Open No.63-134565 for example discloses a method of producing a carbide on thesurface of diamond particles, thereby enhancing the binding force of asintering aid metal to individual diamond particles to ease sintering.Many products of diamond sintered body using sintering aid including atungsten carbide in order to ease sintering are manufactured.

When a carbide is thus generated on the surface of diamond particles,however, the wear resistance, chipping resistance, shock resistance andthermal conductivity are lower than diamond sintered bodies includingonly diamond particles and a ferrous metal. If a tungsten carbide isadded to a sintering aid, the content of the sintering aid increases,which is more likely to deteriorate the wear resistance of the diamondsintered body.

In recent years, harder materials difficult to cut have increased theneed for machining tools with a diamond sintered body for cutting theseharder materials. As a result, it is required that the sintered body hasa wear resistance, a chipping resistance, a shock resistance and athermal conductivity higher than conventional sintered bodies for makingcutting tools.

The present invention is directed to a solution to the above-describedproblems, and it is an object of the present invention to provide adiamond sintered body having a required wear resistance, chippingresistance, shock resistance and thermal conductivity higher thanconventional diamond sintered bodies.

SUMMARY OF THE INVENTION

The inventors have found that the strength such as the chipping andshock resistance, the wear resistance and the thermal conductivity of adiamond sintered body can be improved by strengthening direct bondsbetween the diamond particles and the chipping. Conventionally hardparticles have been used by sintered bodies using granular diamondpowder. Such hard particles have a low compatibility with diamondparticles in order to restrain the growth of the diamond particles.Methods of restraining grain growth without using such hard particleswere considered by the inventors.

As a result, it was found that diamond dissolved in a ferrous metal as asintering aid at the time of sintering, and as the diamond sintered bodycooled down after the sintering, the diamond in the ferrous metal wasre-precipitated, which caused abnormal growth of diamond particles. Itwas then found that in order to prevent this phenomenon, metallictungsten should be added to the ferrous metal as the sintering aid,which reduced the amount of diamond dissolved in the ferrous metal,which could reduce re-precipitation and prevent diamond particles fromgrowing abnormally. By this method, the use of conventional hardparticles is not necessary, diamond particles are more easily bondedwith one another, so that a strong skeleton is formed. Furthermore,since the hard particles are not necessary, the content of diamond inthe resultant diamond sintered body increases.

In a sintered body using coarse-grained diamond powder, metal tungstenadded in a sintering aid makes it easier to sinter the diamondparticles. Therefore, the addition of tungsten carbide as conventionallypracticed is not necessary, which improves the wear resistance of thediamond sintered body.

It was also found that the wear resistance of the sintered bodyincreased as the content of diamond particles in the diamond sinteredbody increased.

It was also found that the size of defects in the sintered body wasclosely related with strength characteristics such as the chippingresistance and shock resistance of the sintered body. The defects hereinare diamond particles having an extremely large size in the sinteredbody, a pool of a sintering aid such as a solvent metal, a fault in thediamond sintered body and the like. The strength of the sintered bodyincreases as defects in the diamond sintered body are reduced.

A high strength and abrasion resistant diamond sintered body accordingto the present invention is based on the above knowledge and includessintered diamond particles, a sintering aid and an inevitable impurityas the remainder. The content of the sintered diamond particles is atleast 80 vol. % and less than 99 vol. %. The diamond particles have aparticle size in the range from at least 0.1 μm to at most 70 μm.Sintered diamond particles next to each other are directly bonded. Thesintering aid includes at least one kind selected from the groupconsisting of iron, cobalt and nickel, and metallic tungsten. Herein,the substance represented by the word “tungsten” may be metallictungsten or a tungsten compound such as tungsten carbide. The content oftungsten in the sintered body is in the range from at least 0.01 wt % toat most 8 wt %.

In such a diamond sintered body, metallic tungsten is added in thesintering aid. As a result, abnormal growth of diamond particles used asa raw material may be restrained without adding hard particles even ifthe size of the diamond particles is small. Meanwhile, if the size ofdiamond particles used as a raw material is large, a highly strongdiamond sintered body having high chipping resistance, wear resistance,shock resistance and thermal conductivity may be provided by addingmetallic tungsten in the sintering aid. Since the amount of thesintering aid to be added is smaller than the conventional cases and thecontent of diamond is larger, the wear resistance will not be lowered.

The content of sintered diamond particles is set in the range from atleast 80% by volume to less than 99% by volume for the following reason.If the content of sintered diamond particles is less than 80 volume %,the strength such as chipping resistance and shock resistance, and thewear resistance are reduced, while the content of diamond particlescannot be technically set to the level equal to or higher than 99% byvolume.

The size of sintered diamond particles is set in the range from at least0.1 μm to at most 70 μm for the following reason. If the size ofsintered diamond particles is less than 0.1 μm, the surface area ofdiamond particles increases, and then a diamond sintered body is morelikely to abnormally grow, which reduces the wear resistance of thediamond sintered body. If the particle size exceeds 70 μm, the cleavageof diamond particles reduces the strength of the diamond sintered body.

The content of tungsten in the sintered body is set in the range from atleast 0.01% by weight to at most 8% by weight for the following reason.If the content of tungsten is less than 0.01% by weight, the effect ofadding metal tungsten in the sintering aid cannot be obtained. If thecontent of tungsten exceeds 8% by weight, the content of diamond in thesintered body is reduced, and the diamond dissolved in the sintering aidis too small, resulting in incomplete sintering.

The diamond sintered body includes tungsten carbide, the ratio(I_(WC)/I_(D)) of X-ray diffraction intensity I_(WC) by the plane index(100) or the plane index (101) of the tungsten carbide in the diamondsintered body relative to X-ray diffraction intensity I_(D) by the planeindex (111) of the sintered diamond particles is less than 0.02, thediamond sintered body contains cobalt, and the ratio (I_(CO)/I_(D)) ofX-ray diffraction intensity I_(CO) by the plane index (200) of cobalt inthe diamond sintered body relative to I_(D) is preferably less than 0.4.

The diamond sintered body contains nickel, and the ratio (I_(Ni)/I_(D))of X-ray diffraction intensity I_(Ni) by the plane index (200) of thenickel in the diamond sintered body relative to X-ray diffractionintensity I_(D) by the plane index (111) of the sintered diamondparticles is preferably less than 0.4.

The diamond sintered body contains iron, and the ratio (I_(Fe)/I_(D)) ofX-ray diffraction intensity I_(Fe) by the plane index (200) of the ironin the diamond sintered body relative to X-ray diffraction intensityI_(D) by the plane index (111) of the sintered diamond particles ispreferably less than 0.2. Herein, the “X-ray diffraction intensity”refers to the level of a peak in an X-ray diffraction profile using aCuKα radiation (a characteristic X-ray generated by the K-shell of Cu).

The above conditions are defined because if I_(WC)/I_(D) exceeds 0.02,the amount of tungsten carbide is excessive, which lowers the wearresistance. If the intensity ratio of the intensity by the above ferrousmetals are without the above-described ranges, the amount of the ferrousmetal in diamond sintered body becomes excessive, which also lowers thewear resistance of the diamond sintered body.

The sintering aid further includes palladium, and the ratio of thepalladium in the sintering aid is preferably in the range from at least0.005 % by weight to at most 40% by weight. In this case, since thepalladium is added to the sintering aid, the melting point of thesintering aid is lowered, so that the diamond sintered body may besintered at low temperatures. The ratio of the palladium is set in therange from at least 0.005% by weight to at most 40% by weight for thefollowing reason. If the ratio of palladium is less than 0.005% byweight, the amount of palladium is not enough for lowing the meltingpoint of the sintering aid, while if the ratio exceeds 40% by weight,the melting point of the sintering aid conversely increases, which makessintering hard.

The sintering aid further includes at least one kind selected from thegroup consisting of tin, phosphorus and boron, and the total percentageof tin, phosphorus and boron in the sintering aid is preferably at least0.01% by weight and at most 30% by weight. In this case, since at leastone kind from tin, phosphorus and boron is included in the sinteringaid, any of these elements lowers the melting point of the sinteringaid. As a result, the diamond powder may be sintered at relatively lowtemperatures. Herein, the ratio of these elements is set in the rangefrom at least 0.01% by weight to at most 30% by weight for the followingreason. If the ratio of these elements is less than 0.01% by weight, theeffect of lowering the melting point of the sintering aid is not enough,while if the ratio exceeds 30% by weight, diamond hardly dissolves inthe ferrous group metal in the sintering aid at the time of sintering.Thus, the bonds between diamond particles will not be enough, and thestrength or thermal conductivity are lowered.

The inventors also noticed oxygen or oxide adsorbed at the surface ofdiamond powder particles in a raw material for manufacturing a diamondsintered body, and found that removal of oxygen or oxide could reducedefects in the sintered body, and the strength of diamond sintered bodycould be improved. As a result, the percentage of oxygen in the diamondsintered body is preferably in the range from at least 0.005% by weightto 0.08% by weight, because ratios less than 0.005% by weight cannot beobtained by presently available techniques, while the strength of thediamond sintered body could be the same as conventional cases for aratio equal to or higher than 0.08% by weight.

Traverse resistance measured at a span of 4 mm, using a measurement testpiece having a length of 6 mm, a width of 3 mm and a thickness in therange from at least 0.35 mm to at most 0.45 mm manufactured from adiamond sintered body obtained as described above is preferably in therange from at least 50 kgf/mm² to 300 kgf/mm².

Traverse resistance measured at a span of 4 mm, using a test piecemanufactured from the diamond sintered body thus obtained and dissolvedin fluoro-nitric acid is preferably at least 50 kgf/mm².

The above-described highly strong and abrasion-resistant diamondsintered body is preferably used as a tool. In this case, the toolincluding the highly strong and abrasion-resistant diamond sintered bodyincludes sintered diamond particles, and a sintering aid and aninevitable impurity as the remainder. The content of the sintereddiamond particles is in the range from at least 80% volume by volume toless than 99% by volume. The sintered diamond particles have a particlesize in the range from at least 0.1 μm to at most 70 μm. Sintereddiamond particles next to each other are directly bonded. The sinteringaid includes at least one kind selected from the group consisting ofiron, cobalt and nickel, and metallic tungsten. The content of thetungsten in the sintered body is in the range from at least 0.01% byweight to at most 8% by weight.

In order to provide a diamond sintered body according to the presentinvention, a sintering aid is homogeneously distributed in the sintereddiamond particles and does not contain unnecessary components. As amethod of coating particles included in diamond powder with a sinteringaid in view of the above points, CVD (Chemical Vapor Deposition) methodsand PVD (Physical Vapor Deposition) methods or solution precipitationmethods may be employed.

Furthermore, since homogeneously distributing of the sintering aidcoating the surface of diamond particles is significantly important forimprovements in the difficulty of sintering diamond powder and thestrength of the diamond sintered body according to the presentinvention, and the method should be highly economical, an electrolessplating disclosed in Japanese Patent Laying-Open No. 8-225875 by theinventors may be most preferably employed.

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

Manufacture of Diamond Sintered Body

Different kinds of diamond powder having different particle sizes andsintering aids having different components (IA to IH) given in Table 1were prepared. Sintering aids 1A, 1B, 1E and 1F were added to diamondpowder by eletroless plating, sintering aids 1C and 1G by ultrafineparticle powder mixing, and sintering aids 1D and 1H by cemented carbideballmilling. For the ultrafine powder mixing, ultrafine cobalt powderhaving a particle size of at most 0.5 μm and diamond powder were placedin a container formed of Teflon to have a prescribed composition, andthen Teflon balls were placed in the container, and then they were mixedfor three hours to manufacture a powder sample. For the cemented carbideballmilling, diamond powder, tungsten carbide powder and cobalt powderwere placed in a container formed of tungsten carbide-cobalt togetherwith tungsten carbide-cobalt balls for mixing for a prescribed timeperiod. The time for mixing was controlled to manufacture sample powderhaving a prescribed sintering aid composition. The samples by thesemethods are given in Table 1.

TABLE 1 Diamond Method of Sam- Powder Adding Content of Composition ofple Particle Sintering Sintering Aid Sintering Aid No. Size (μm) Aid (%by vol) (% by wt) 1A 0.1 ˜ 4  electroless 7.0 90.85 Co, 5.0 W, 4.0plating Fe, 0.05 Pd, 0.10 Sn 1B 0.1 ˜ 4  electroless 25.0 90.85 Co, 5.0W, 4.0 plating Fe, 0.05 Pd, 0.10 Sn 1C 0.1 ˜ 4  ultrafine 7.0 100 Coparticle powder mixing 1D 0.1 ˜ 4  cemented 7.0 25 Co, 75 Wc, carbideballmill 1E 0.1 ˜ 60 electroless 7.0 90.85 Co, 5.0 W, 4.0 plating Fe,0.05 Pd, 0.10 Sn 1F 0.1 ˜ 60 electroless 25.0 90.85 Co, 5.0 W, 4.0plating Fe, 0.05 Pd, 0.10 Sn 1G 0.1 ˜ 60 ultrafine 7.0 100 Co particlepowder mixing 1H 0.1 ˜ 60 cemented 7.0 25 Co, 75 WC, carbide ballmill

The “Composition of sintering aid” in Table 1 refers to the percentageof each component in the sintering aid. For example, in the case labeled“90.85 Co”, 90.85% by weight of the sintering aid is cobalt.

Samples 1A to 1D were heat-treated at 1300° C. for 60 minutes, and 1E to1H were heat-treated at 1500° C. for 60 minutes. Samples 1A to 1H wereeach placed in a tantalum container, and sintered under a pressure of 55kb, at a temperature of 1450° C. using a belt type ultra high pressureapparatus to provide a diamond sintered body.

Evaluation of Diamond Sintered Body

Measurement of Diffraction Intensity Ratio

The diamond sintered body obtained by the above process was subjected toX-ray diffraction an electron beam at an acceleration voltage of 40 kVdirected to a copper target, at a current of 25 mA, at a diffractionangle 2θ in the range from 20° to 80°, and at a scanning speed of0.1°/sec, using a CuKα radiation (a characteristic X-ray generated bythe K-shell of Cu). As a result, the levels (of intensity) I_(WC),I_(D), and I_(CO) of diffraction peaks of the plane index (101) oftungsten carbide, the plane index (111) of diamond, and the plane index(200) of cobalt were measured.

Measurement of Strength

A plurality of rectangular parallelepiped test pieces having a length of6 mm, a width of 3 mm, and a thickness of 0.4 mm were cut from eachdiamond sintered body. The strength (transverse rupture strength) of thesintered body was measured by a three-point bending test at a spandistance of 4 mm for these samples. The samples were placed in afluoronitric acid solution produced by mixing 40 ml nitric acid of amolarity of 30% and 10 ml hydrogen fluoride of a molarity of 45%. Thesesamples were each placed in a sealed container, maintained at 130° C.for three hours for dissolution. The strength (transverse rupturestrength) of the sintered bodies was measured by a three-point bendingtest at a span distance of 4 mm for the samples subjected to and notsubjected to the dissolution treatment.

Measurement of W Content

The total contents of metallic tungsten (W) and tungsten carbiderelative to the weight of the diamond sintered body were measured byplasma emission spectrochemical analysis.

Measurement of Diamond Content

The surface of the diamond sintered body was observed using amicroscope, and the region of diamond particles was measured todetermine the diamond content in the sintered body.

Evaluation of Cutting Performance

A tool for cutting is manufactured using the sintered body, and thecutting performance was evaluated under the following condition.

Workpiece: Al-16% by weight Si alloy round bar

The rotating speed of the surface of the workpiece: 700 m/min

Depth of cut: 0.5 mm

Feed rate: 0.15 mm/rev

Cutting time: 5 min

Confirming the Presence of Metallic Tungsten

Samples to be observed by a transmission electron microscope weremanufactured from the obtained sintered bodies, observed in a pluralityof arbitrary fields of view, and the presence/absence of metallictungsten was determined based on the electron diffraction pattern. Theresult is given in Table 2.

TABLE 2 Strength Flank X-ray Diffraction (kgf/mm²) W Diamond Wear SampleIntensity Ratio (%) Before After Content Content Width Metallic No.I_(WC)/I_(D) I_(CO)/I_(D) Treated Treated (% by wt) (% by vol) (μm)Tungsten 1A 0.1 31 256 142 4.1 86 81 ◯ 1B 0.9 45 210 117 4.5 80 103 ◯ 1CSintering not possible 1D Sintering not possible 1E 0.1 17 121 82 1.7 9666 ◯ 1F 0.2 25 103 71 1.9 91 73 ◯ 1G 1.8 28 87 59 2.1 83 Chipping X 1H12 31 95 68 6.2 88 79 X ◯: metallic tungsten present X: absent

The “W content” in Table 2 represents the percentage by weight oftungsten (metallic tungsten and tungsten carbide in total) in thesintered body. The presence and absence of metallic tungsten observed bythe transmission electron microscope was represented by “◯” and “×” inthe Table.

As can be seen from Table 2, products 1A and 1E according to the presentinvention show good performances both in the strength and flank wear.

Meanwhile, for 1C and 1D, the sintering aid was insufficient in amountand heterogeneously distributed, and therefore the dissolution of thesintering aid did not occur homogeneously within the powder diamond, sothat a complete sintered body was not obtained.

It was observed that the sintering aid was heterogeneously distributedin the microstructure of the sintered body 1G, which caused chipping inthe tool while cutting, and the tool could no longer be used.

As a result, products 1A and 1E according to the present inventionprovided higher strength, a smaller flank wear width and higher chippingresistance than conventional products 1D and 1H, and would show betterperformance as a good cutting tool. As a result of the observation withthe microscope, sintered diamond particles next to each other weredirectly bonded.

Second Embodiment

Experiments to compare the characteristic of sintered bodies dependingupon the particle sizes of diamond particles were performed. Severaldiamond powder samples having various particle sizes was prepared. Asintering aid was added to the diamond powder by an electroless platingsuch that the ratio of the diamond powder is 93% by volume and the ratioof a sintering aid having a prescribed position is 7% by volume, thenheat treated, and diamond sintered bodies were manufactured according tothe same method as the first embodiment.

The strength and flank wear width of the diamond sintered bodies weremeasured according to the method the same as the first embodiment. Theresult is given and Table 3.

TABLE 3 Diamond Composition Flank Power Diamond of Sintering Wear WSample Particle Content Aid Strength Width Content Metallic No. Size(μm) (% by vol) (% by wt.) (kgf/mm²) (μm) I_(WC)/I_(D) (% by wt)Tungsten 2A 0.1 ˜ 4  83 94.85 Co, 5.0 238 91 0.5 4.3 ◯ W, 0.05 Pd, 0.10Sn 2B 0.1 ˜ 60 93 94.85 Co, 5.0 105 67 0.2 2.1 ◯ W, 0.05 Pd, 0.10 Sn 2C20 ˜ 100 96 94.85 Co, 5.0 45 chipping 0.1 1.2 ◯ W, 0.05 Pd, 0.10 Sn ◯:metallic tungsten present X: absent

In a product 2A, the content of diamond was reduced, because muchdiamond was dissolved in the sintering aid, while in 2C, the sinteringaid flowed out, and therefore the content of diamond increased. As canbe seen from Table 3, a sample with a smaller diamond particle size, inother words, a finer sample (2A) has higher strength, and thereforehigher shock resistance. Meanwhile, a sample with a larger particlesize, in other words, a sample with coarse particles (2B) has a smallerwidth of flank wear, and has higher wear resistance. In 2C, the diamondparticle size was so large that chipping was caused during cutting andthe cutting test could not be continued.

Third Embodiment

Experiments about characteristics of sintered bodies depending upon theamount of metallic tungsten added in the sintering aid were performed.Several diamond powder samples having various particle sizes wereprepared. Sintering aids having various ratios of tungsten were added todiamond powder samples by electroless plating, and subjected to heattreatment, followed by sintering according to the method the same as thefirst embodiment to obtain diamond sintered bodies. For the obtaineddiamond sintered bodies, the strength and flank wear width were measuredaccording to the method the same as the first embodiment. The result isgiven in Table 4.

TABLE 4 Flank Diamond Composition of Diamond Wear W Sample ParticleSintering aid Content Strength Width Content Metallic No. Size (μm) (%by wt) (% by vol) (kgf/mm²) (μm) (% by wt) I_(WC)/I_(D) Tungsten 3A 0.1˜ 4  90.85 Co, 5.0 W, 86 256 81 4.1 0.1 ◯ 4.0 Fe, 0.05 Pd, 0.10 Sn 3B0.1 ˜ 4  80.85 Co, 15.0 W, 79 186 110 13.4 2.1 ◯ 4.0 Fe, 0.05 Pd, 0.10Sn 3C 0.1 ˜ 4  95.85 Co, 4.0 Fe, Abnormal Grain growth 0.05 Pd, 0.10 Sn3D 0.1 ˜ 60 90.85 Co, 5.0 W, 96 121 66 1.7 0.1 ◯ 4.0 Fe, 0.05 Pd, 0.10Sn 3E 0.1 ˜ 60 80.85 Co, 15.0 W, 90 103 85 8.2 1.7 ◯ 4.0 Fe, 0.05 Pd,0.10 Sn 3F 0.1 ˜ 60 95.85 Co, 4.0 Fe, Partly not sintered 0.05 Pd, 0.10Sn ◯: metallic tungsten present X: absent

Samples 3A and 3D in Table 4 are diamond sintered bodies manufacturedfrom the same powder as samples 1A and 1E manufactured according to thefirst embodiment. Samples 3B, 3C, 3E and 3F were produced by changingthe amount of metallic tungsten added in the sintering aid.

It is appreciated that when the amount of tungsten in the sintering aidexceeds 8% by weight like samples 3B and 3E, the “strength” is smallwhile the “width of flank wear” is large, and therefore the strength orwear resistance is lowered. For samples 3C and 3F without addingmetallic tungsten, sintering was often incomplete and sintered body wasnot stably obtained. It is appreciated that samples 3A and 3D in whichthe amount of tungsten added in the sintered bodies is at least 0.01% byweight and at most 8% by weight have high strength and wear resistance.

Fourth Embodiment

Experiments were performed about the effect of the amount of palladiumadded in the sintering aid on the stability of obtaining completesintered body. Several diamond powder samples having various particlesizes were prepared. The powder samples were formed by adding asintering aid containing tungsten and palladium in various ratios, ironin 4.0% by weight, and tin in 0.1% by weight with the remainder ofcobalt. These samples were maintained at a temperature of 1450° C. undera pressure of 50 kb for 20 minutes, using a belt type ultra highpressure apparatus. The result is given is Table 5.

TABLE 5 W Content Pd Content Diamond Powder Particle Size (μm) (% by wt)(% by wt) 0.1 ˜ 1 1 ˜ 2 5 ˜ 10 4.0 — ◯ (3.8) ◯ (3.5) ◯ (2.9) 4.0 0.02 ◯(3.7) ◯ (3.2) ◯ (2.5) — 0.02 Δ ◯ ◯ (particle growth) — — X X ◯Parenthesized numbers each represent the content of tungsten (% by wt).

The “◯” in Table 5 indicates that the powder sample was sintered and theparticles did not grow abnormally. The “Δ (particles growth)” indicatesthat the powder sample was sintered but part of the diamond particlesgrew abnormally. The “×” indicates that the powder sample was notcompletely sintered. For the samples with addition of metallic tungsten,the result of analysis of the content of tungsten in the sintered bodyis indicated in parentheses in the table. As can be seen from Table 5,in a sample including only tungsten and a sample including tungsten andpalladium, the sintering was surely performed. In a sample withouttungsten and including palladium, the sintering was performed to acertain extent, but the sintering was not performed sufficiently if finediamond powder was used. This shows that the sintering is easilyperformed if the content of palladium is at least 0.01% by weight and atmost 40% by weight, which is the range according to the presentinvention.

Fifth Embodiment

Experiments were performed about characteristics of sintered bodiesproduced with an additional sintering aid. Several diamond powdersamples having a particle size in the range from 0.1 to 30 μcm wereprepared. The diamond powder samples were subjected to degreasing andacid cleaning in order to add a sintering aid by electroless plating.The diamond powder samples were immersed in a cold solution containingpalladium chloride, stannous chloride and hydro-chloric acid for twominutes at room temperature as a pre-treatment. Subsequently, thediamond powder samples were immersed in a sulfuric acid aqueous solutionfor two minutes. Then, the samples were washed with water, and thenimmersed in a Ni-B aqueous solution for plating at a temperature of 90°C. containing nickel chloride and sodium boron hydroxide for two minutesto provide diamond powder samples coated with the sintering aid.

After the diamond powder samples were compressed for shaping, a metalplate and as an additional sintering aid having a composition given inTable 6 and the compact were layered and enclosed in a tantalumcontainer.

TABLE 6 Diamond Amount of Composition Powder Sintering Aid Compositionof Additional Sample Particle for Coating of Sintering Sintering Aid No.Size (μm) (% by vol) Aid (% by wt) (% by wt) 4A 0.1 ˜ 30 0.1 87.0 Ni,100 Ni 7.0 Pd, 5.0 W, 1.0 Sn 4B 0.1 ˜ 30 0.1 87.0 Ni, 98 Ni, 2.0 B 7.0Pd, 5.0 W, 1.0 Sn 4C 0.1 ˜ 30 0.1 87.0 Ni, 89 Ni, 11 B 7.0 Pd, 5.0 W,1.0 Sn 4D 0.1 ˜ 30 0.1 87.0 Ni, 79 Ni, 21 B 7.0 Pd, 5.0 W, 1.0 Sn 4E 0.1˜ 30 0.1 87.0 Ni, 66 Ni, 34 B 7.0 Pd, 5.0 W, 1.0 Sn

The “composition of additional sintering aid ” in Table 6 is thecomposition of the metal plate. The “amount of sintering aid forcoating” represents the ratio of the sintering aid in the diamondsintered body in percentage by volume.

Subsequently, the tantalum container was maintained at a temperature of1550° C. and under a pressure of 60 kb for 10 minutes using a girdletype ultra high pressure apparatus. As a result, each diamond sinteredbody was produced.

Each of the sintered bodies was processed into a test piece having alength of 6 mm, a width of 3 mm and a thickness of 0.3 mm, followed bythree-point bending test at a span distance of 4 mm to evaluate thestrength. The result is given in Table 7.

TABLE 7 Diamond Total Content of Sn Sample Content and B in SinteringStrength No. (% by vol) Aid (% by wt) (kgf/mm²) 4A 94 0.005 88 4B 941.99 118 4C 94 11.0 105 4D 94 20.9 94 4E 94 33.8 72

As can be seen from Table 7, the strengths of 4B, 4C and 4D are higherthan those of 4A and 4E.

More specifically, the total content of tin, phosphorus and boron in asintering aid is preferably at least 0.01% by weight and at most 30% byweight. When the same experiments were performed with a sintering aidcontaining tin, phosphorus and boron, it was found that the totalcontent of these substances was preferably at least 0.01% by weight andat most 30% by weight.

Sixth Embodiment

Experiments were performed about characteristics of diamond sinteredbodies while the heat treatment temperature of the diamond powdersamples was varied. Products 1A and 1E produced according to the firstembodiment were heat-treated under various conditions. Then, diamondsintered bodies were produced by sintering the powder subjected to theheat treatment under the conditions the same as those of the firstembodiment. The strength of the diamond sintered bodies was measuredaccording to the same method as that in the first embodiment, and thecontent of oxygen in the sintered bodies were measured by plasmaemission spectrochemical analysis. The result is given in Table 8.

TABLE 8 Sample Heat Treatment Strength Oxygen Content No. Condition(kgf/mm²) (% by wt) 5A-1 1300° C., 60 min 256 0.025 5A-2 1200° C., 60min 207 0.110 5A-3 1100° C., 60 min 184 0.143 5E-1 1500° C., 60 min 1210.009 5E-2 1400° C., 60 min 105 0.015 5E-3 1300° C., 60 min  88 0.022

In Table 8, samples 5A-1 to 5A-3 were obtained by using the first powderexample 1A shown in Table 1. Samples 5E-1 to 5E-3 were obtained by usingthe powder example 1E of Table 1. Table 8 shows that the amount ofoxygen remaining in the sintered body tends to decrease and thereforethe strength of the sintered body increases as the heat treatmenttemperature is raised.

Note that it was appreciated from another experiment that powder sample1A was not appropriately used, because the surface of the diamond powderwas extremely graphitized when heat-treated at a high temperature equalto or higher than 1400° C., which causes graphite to remain in theresultant sintered body so that the sintering and cutting performancewere lowered.

Seventh Embodiment

A diamond powder sample having a particle size in the range from 0.1 to15 μm was prepared, and a sintering aid identical to that added topowder samples 1A according to the first embodiment was added, followedby heat treatment at 1300° C. in a vacuum. Subsequently, the powderafter the heat treatment was filled within a container of an alloycontaining tungsten carbide in 10% by weight and having an outerdiameter of 20 mm, an inner diameter of 12 mm and a height of 18 mm,followed by sintering at a high pressure and high temperatureconditions. Wire drawn dies having a line size diameter of 3 mm weremanufactured from the resultant sintered body. The dies was used for awire drawing test for a copper-plated steel wire at a speed of 500m/min, with a water-soluble lubricant. As a result, an 80 ton-steel wirewas produced by wire drawing, and the surface of the wire was fine.

Eighth Embodiment

Diamond sintered bodies 1A and 1E according to the first embodiment wereused to manufacture a circular throw-away tip having a diameter of 13.2mm and a thickness of 3.2 mm, and a round bar of granite having acompression strength of 1500 kg/cm² was cut by a general purpose latheunder the following conditions:

The rotating speed of the surface of workpiece to be cut: 180 m/min

Depth of cut: 0.5 mm

Feed rate: 0.25 mm/rev

Cutting time: 3 min

As a result, no chipping was observed in diamond sintered body 1A, andthe flank abrasion width was above 0.5 mm. Meanwhile, in diamondsintered body 1E, chipping as large as 0.03 mm was observed at thecutting edge, while the flank wear width was as small as 0.1 mm, whichis small enough for the cutting test to be continued.

When a tool manufactured from a conventional diamond sintered body wasused for cutting, the cutting resistance increases by abrasion at thetime point after cutting for about 2 minutes, abnormal noises were heardduring cutting, and therefore the cutting could not be continued.Extreme flank wear was observed in the used tool, and there was acracking reaching to the cemented carbide which supports the diamondsintered body.

When the diamond sintered body according to the present invention wasapplied to a drill bit tool which required shock resistance, goodresults were brought about.

Ninth Embodiment

Several diamond powder samples having a particle size in the range from0.1 to 60 μm were provided with a sintering aid containing cobalt,tungsten, iron and palladium in various percentages by electrolessplating, followed by a heat treatment and then sintering. The obtainedvarious sintering bodies were subjected to X-ray diffraction as is thecase with the first embodiment, the diffraction intensity I_(Ni) by theplane index (200) of nickel, the diffraction intensity I_(Fe) by theplane index (200) of iron and the diffraction intensity I_(D) by theplane index (111) of diamond particles were measured and the ratiosI_(Ni)/I_(D) and I_(Fe)/I_(D) were obtained. The strength and flankabrasion width of each of the sintered bodies was checked similarly tothe first embodiment.

As a result, the samples with I_(Ni)/I_(D) of less than 0.4 orI_(Fe)/I_(D) less than 0.4 had high strength and a small width of flankwear.

INDUSTRIAL APPLICABILITY

A highly strong and highly abrasion-resistant diamond sintered bodyaccording to the present invention may applied to cutting tools such asa milling cutter, and an end mill, abrasion-resistant tools such as wiredrawn dies, and shock-resisting parts such as a golf club head and ashock type power grinding jig.

What is claimed is:
 1. A high strength and high wear resistance diamondsintered body comprising sintered diamond particles having a particlesize in the range of 0.1 μm to 70 μm, said sintered diamond particlesbeing present in said diamond sintered body within the range of at least80% by volume to less than 99% by volume, wherein said sintered diamondparticles are directly bonded to one another, said diamond sintered bodyfurther comprising oxygen within the range of at least 0.005% by weightto less than 0.08% by weight, at least one of metallic tungsten and atungsten compound within the range of at least 0.01% by weight to atmost 8% by weight, and at least one sintering aid selected from thegroup consisting of iron, cobalt and nickel, said sintered diamond bodyfurther comprising unavoidable impurities as a remainder.
 2. The diamondsintered body of claim 1, comprising cobalt having an X-ray diffractionintensity I_(CO) relative to a plane index (200) of said cobalt, saiddiamond sintered body further comprising tungsten carbide having anX-ray diffraction intensity I_(WC) relative to a plane index (100 or101) of said tungsten carbide, said sintered diamond particles having anX-ray diffraction intensity I_(D) relative to a plane index (111) ofsaid sintered diamond particles, wherein a first ratio of I_(WC) toI_(D) is less than 0.02, and wherein a second ratio of I_(CO) to I_(D)is less than 0.4.
 3. The diamond sintered body of claim 1, comprisingnickel having an X-ray diffraction intensity I_(Ni) relative to a planeindex (200) of said nickel, wherein said sintered diamond particles havean X-ray diffraction intensity I_(D) relative to a plane index (111) ofsaid sintered diamond particles, and wherein a ratio of I_(Ni) to I_(D)is less than 0.4.
 4. The diamond sintered body of claim 1, comprisingiron having an X-ray diffraction intensity I_(Fe) relative to a planeindex (200) of said iron, wherein said sintered diamond particles havean X-ray diffraction intensity I_(D) relative to a plane index (111) ofsaid sintered diamond particles, and wherein a ratio of I_(Fe) to I_(D)is less than 0.2.
 5. The diamond sintered body of claim 1, furthercomprising palladium as part of said sintering aid, said palladium beingpresent in said sintering aid within a range of at least 0.005% byweight to at most 40% by weight of said sintering aid.
 6. The diamondsintered body of claim 1, further comprising, as part of said sinteringaid, at least one element selected from the group consisting of tin,phosphorus, and boron, and wherein the total percentage of said tin,phosphorus and boron in said sintering aid is within the range of atleast 0.01% by weight to at most 30% by weight of said sintering aid. 7.The diamond sintered body of claim 1, having a transverse rupturestrength within the range of at least 50 kgf/mm² to at most 300 kgf/mm²as measured on a test piece at a span of 4 mm, said test piece having alength of 6 mm, a width of 3 mm and a thickness within the range of atleast 0.35 mm to at the most 0.45 mm.
 8. The diamond sintered body ofclaim 7, wherein said transverse rupture strength as measured at saidspan of 4 mm is at least 50 kgf/mm² using a test piece dissolved by afluoro-nitric acid.
 9. A tool made of a diamond sintered body as definedin claim 1.